In recent years, from interest in energy conservation, the reduction of power consumption in a variety of devices and efficiency enhancement of a power supply system are being promoted. Also for a power supply apparatus such as an AC/DC conversion apparatus mounted in a variety of devices, efficiency enhancement of power conversion is requested. In a general power supply apparatus, efficiency characteristics of power conversion tend to vary with an output power (a magnitude of a load). In a low load range where an output power of the power supply apparatus is small, consumption of power necessary to drive the power supply apparatus itself appears as a lowering factor (a loss) of power conversion efficiency. On the other hand, in a high load range where an output power of the power supply apparatus is large, output current increases and therefore, a loss due to impedance in the circuit, iron loss, copper loss, and the like appear as lowering factors of power conversion efficiency. In response to such power consumption variations, enhancement of power conversion efficiency of the entire power supply system is requested. There is known a technique for changing the number of power supply apparatus to be operated or a technique for switching over power conversion apparatus of different types to be operated in a high load range and in a low load range of the power supply apparatus in order to enhance power conversion efficiency.
Related arts existing prior to the present application include, for example, the following patent literature.
Patent literature 1 (Japanese Translation of PCT International Application Publication No. 2013-504986) discloses a technique such that in a power supply system configured to connect a plurality of power supply apparatuses in parallel to a load, the number of power supply apparatuses to be operated is changed on the basis of power consumption consumed at a load. The technique disclosed in the patent literature 1 prevents lowering of power conversion efficiency of the entire power supply system by the above technique.
Patent literature 3 (Japanese Laid-open Patent Publication No. 2009-254082) discloses a technique such that in a power supply system configured to make a power supply apparatus redundant, a combination of power supply apparatus for supplying power to a load is selected, based on power conversion efficiency of each of the power supply apparatus, and power consumption at the load.
Patent literature 4 (Japanese Laid-open Patent Publication No. 1993(H05)-091660) discloses a technique such that in a power supply system configured to connect a plurality of power supply apparatuses to a load, one power supply apparatus whose power conversion efficiency is highest is selected on the basis of power consumption at a load.
Power conversion efficiency is expressed as a ratio between input power and output power. The applicant of the present application has proposed a method of calculating an input power with use of a measurement result of output power, which is easily measurable, in patent literature 2 (Japanese Laid-open Patent Publication No. 2011-022022).